[PATCH v2 1/2] dt-bindings: dma: Add Apple ADMAC

[Martin Povišer]

> On 14. 4. 2022, at 19:23, Martin Povišer <povik at cutebit.org> wrote:
> 
>> 
>> On 14. 4. 2022, at 17:43, Rob Herring <robh at kernel.org> wrote:
>> 
>> On Tue, Apr 12, 2022 at 12:22:03AM +0200, Martin Povišer wrote:
>>> Apple's Audio DMA Controller (ADMAC) is used to fetch and store audio
>>> samples on SoCs from the "Apple Silicon" family.
>>> 
>>> Signed-off-by: Martin Povišer <povik+lin at cutebit.org>
>>> ---
>>> 
>>> After the v1 discussion, I dropped the apple,internal-irq-destination
>>> property and instead the index of the usable interrupt is now signified
>>> by prepending -1 entries to the interrupts= list. This works when I do
>>> it like this:
>>> 
>>> interrupt-parent = <&aic>;
>>> interrupts = <AIC_IRQ 0xffffffff 0>,
>>> <AIC_IRQ 626 IRQ_TYPE_LEVEL_HIGH>;
>> 
>> 
>> BTW, just use '-1'. dtc takes negative values (and other expressions).
> 
> Ha! <-1> didn’t work for me but <(-1)> does.
> 
>> 
>>> 
>>> I would find it neat to do it like this:
>>> 
>>> interrupts-extended = <0xffffffff>,
>>> <&aic AIC_IRQ 626 IRQ_TYPE_LEVEL_HIGH>;
>>> 
>>> but unfortunately the kernel doesn't pick up on it:
>>> 
>>> [ 0.767964] apple-admac 238200000.dma-controller: error -6: IRQ index 0 not found
>>> [ 0.773943] apple-admac 238200000.dma-controller: error -6: IRQ index 1 not found
>>> [ 0.780154] apple-admac 238200000.dma-controller: error -6: IRQ index 2 not found
>>> [ 0.786367] apple-admac 238200000.dma-controller: error -6: IRQ index 3 not found
>>> [ 0.788592] apple-admac 238200000.dma-controller: error -6: no usable interrupt
>> 
>> We should make this case work. It is less fragile IMO as it doesn't 
>> depend on the provider's translation of cells.
> 
> Then I may send some patch to that end.

Turns out there’s no need. Passing in <0> in place of a phandle reference
looks like what we want:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/of/base.c?h=v5.18-rc2#n1334

(Confirmed by testing to do the right thing with the IRQs.)

Martin